The present disclosure relates to a clamping system for connecting two tubes together in sealed manner, the facing ends of the two tubes having clamping surfaces that project relative to the cylindrical outside surfaces of said tubes, the system comprising a collar having a band suitable for co-operating with said clamping surfaces and means for tightening said band, the band having a first flank and a second flank between which an inside trough is defined that is suitable for receiving the clamping surfaces.
A clamping system of this type is known from European Patent No. EP 1 451 498. The cross-section of the band of the collar is, for example, substantially V-shaped or U-shaped, so that the branches formed by the cross-sectional shape bear respectively against the clamping surface of the first tube and against the clamping surface of the second tube. Thus, tightening the collar tends to hold the tubes clamped one against the other. A V-shaped cross-section is advantageous insofar as, when the collar is tightened, it urges the tubes together.
For example, the means for tightening the band of the collar comprise a nut-and-bolt system. Thus, the ends of the band can be turned out so as to form bearing tabs provided with holes through which a bolt can be inserted. The head of the bolt is retained relative to one of said tabs, while a nut is retained relative to the other tab, so that the bolt and the nut being turned relative to each other causes the band to be tightened. However, other tightening means may be provided, e.g. of the type operating by hooking, and in particular of the type comprising a hook that is turned out relative to the band and a lug also turned out relative to the band, the hook hooking behind the lug to keep the collar in the tightened state. In EP 1 451 498, the clamping system further comprises a washer that is secured to the collar by means of fastening tabs provided on the washer, which also has tabs suitable for holding onto the first tube when the collar is pre-attached to the end of said first tube. In the meaning of the present description, “pre-attached” means that the tube is merely engaged into the collar, without said collar being tightened. Thus, retaining the collar in the pre-attached state around the end of the first tube makes it possible to keep it on standby before butting the two tubes together and tightening the band of the collar around their assembled-together ends.
European Patent No. EP 2 598 785 proposes equipping the system with first and second pre-attachment means for pre-attaching the collar to the first and second tubes, once they have been brought together and engaged in the collar. That makes it possible to tighten the band without having to hold the two tubes in position. In that patent, the first and second pre-attachment means may be formed on a single washer carried by the band of the collar, in particular by its first flank, or indeed by two washers, namely a first washer analogous to the washer of the system described in Patent EP 1 451 498, and carried by the first flank, and a second washer carried by the second flank.
The above-mentioned devices are generally satisfactory, but they require one or two washers to be used to achieve the pre-attachment. Since those washers have inside peripheries that are analogous to the inside periphery of the collar, they represent a relatively large quantity of material. In addition, their geometrical shapes are relatively complex so as to enable them not only to be held correctly relative to the band of the collar over their entire peripheries, but also to retain the ends of the respective tubes with which they co-operate correctly relative to the collar. In addition, under certain circumstances, the washer needs to also provide a function other than the pre-attachment function, e.g. a sealing function. Under certain circumstances, that function can be provided only if the washer has a precise thickness, which is not always compatible with the springiness that the pre-attachment tabs need to have in order to perform their function, it being understood that, in principle, said tabs have the same thickness as the washer because they are made from the same strip of material.
In the particular situation of the tubes being assembled together by a ball joint, U.S. Pat. No. 7,770,937 is also known and it recommends, for achieving the pre-attachment, either welding one of the tubes to an axial bracket that is retained relative to the band of the collar, or welding the band of the collar to a clip that extends over a portion of the circumference of said band and that has fingers that come to hook behind the clamping surface of one of the tubes. That patent also suggests using individual fingers fastened to the band in such a manner as to form extensions that extend relative to the edge of said band and that can come to hook onto the clamping surface of a tube. Such individual fingers are only provided outside the band, and, like the clip, they are welded to the outside periphery of the band. Thus, the pre-attachment means that U.S. Pat. No. 7,770,937 proposes are relatively voluminous on the outside of the collar and suffer from the drawback of requiring a welding operation either on the outside periphery of the collar, or on one of the tubes. Naturally, such an operation requires that the appropriate material is available, either on the production line on which the collar is manufactured, or on the assembly line on which the collar is assembled with the tubes. Welding is an operation that is very distinct from the other operations required for manufacturing the collar or for assembling it with the tubes, and can damage the surface of the parts in question.